sp: avoid masking uuid in StoragePool methods

For some unknown reason during an unrelated refactoring these methods
began to trigger pep8 errors related to the uuid variable masking the
module with the same name.

Change-Id: I4d108e9daa42290c46faa1de3d43e8883487e83c
Signed-off-by: Federico Simoncelli <fsimonce@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/21873
Reviewed-by: Dan Kenigsberg <danken@redhat.com>